package 每日一题;

import java.util.Scanner;

public class WY16不要二 {
    public static void main(String[] args) {
        //本体的关键是 根据欧几里得距离不等于2，
        //推断出当前位置arr[i][j]的arr[i+2][j]和arr[i][j+2]不能放蛋糕
        Scanner sc=new Scanner(System.in);
        int row=sc.nextInt();
        int column=sc.nextInt();

        int res=0;
        int[][] arr=new int[row][column];
        for (int i = 0; i <row; i++) {
            for (int j = 0; j <column; j++) {
                if (arr[i][j]==0) {
                    res++;
                    if (i+2<row) {
                        arr[i+2][j]=1;
                    }
                    if (j+2<column){
                        arr[i][j+2]=1;
                    }
                }
            }
        }
        System.out.println(res);
    }
}
